A sub frame will get you there quickly and cheaply.
Up grades can be made as needed like "strong arm" control arms bigger rotors etc.Just throwing a cross member in is not as quick or strong as a boxed camero sub frame(without lots of extra work) to the original frame and thousands more expensive... You can get a complete sub frame for 100-200.00...Even a completely rebuilt one is MUCH cheaper than an aftermarket unit,But anything will be better than the straight Axel and leaf spring suspension....They don't even make a good boat anchor....I 'd get rid of the steering box and all the linkage too and use a power rack from a 95 or so camero.....If I was to order something(aftermarket) already made, I would get the "Whole" frame and suspension (subframe) from fatmans or a company like them.